Frequency Distribution

In the previous section, the mean seasonal and annual patterns of temperature distribution in the Arctic in the period 1951-1990 have been presented. Also knowledge about the occurrence frequency of different temperature intervals is particularly useful, especially for weather and climate forecasting. Przybylak (1996a) investigated this problem using both data from individual stations and area-average for climatic regions (see Figure 1.2). The results for such data are very similar. Figure 4.9 presents the relative frequency of occurrence of mean winter, summer, and annual temperatures of five analysed climatic regions and for the Arctic as a whole in 1°C intervals. Climatic regions where cyclonic activity dominates (Atlantic, Pacific, and Baffin Bay regions) have the greatest variability of mean winter temperature. Their frequency distributions are characterised by a wide range and a more steady occurrence frequency of individual temperatare intervals. Usually the occurrence of three intervals (from -14°C to -17°C) both in the Atlantic (about 70%) and Baffin Bay (about 40%) regions is not accidental, The cyclones, which are connected with the Icelandic low and have the same physical characteristics, are directed simultaneously, as we know, to the Atlantic and Baffin Bay regions. fn the Baffin Bay region, however, the dominance of these cyclones and their strength is lower. As a result, the occurrence frequency of these three intervals is almost twice as low as in the Atlantic region. The most normal frequency distribution shows the mean temperature for the Siberian region, where two intervals markedly dominate: -29°C to -30°C (35%) and 30°C to -31°C (about 20%). There is a 50% chance that the mean winter temperature of the whole Arctic will be between -2I°C and -22°C. There is also a high frequency (about 30%) that the interval 20°C to -21°C will occur.

In summer, the mean temperature of all the climatic regions and of the Arctic as a whole has clear normal frequency distributions. In every region one interval occurs with a frequency of at least 45%. The lowest range of temperature variability occurs in the Atlantic region (only three intervals). Przybylak (1996a) reported that this is caused by the influence of atmospheric circulation, which is still strong in this season. In summer (opposite to winter), the thermal differentiation of air masses incoming here from different directions is markedly lower (Przybylak 1992a). There is as much as a 70% chance that the mean Arctic temperature will range from 3-4°C.

The frequency distribution of the mean annual temperatures, similar to the summer temperature, is nearly normal. The mean annual Arctic temperature in about 95% of cases oscillates between -9°C and -11°C. What is interesting is that such mean annual temperatures do not occur in any climatic region. They are either warmer (Atlantic and Baffin Bay regions) or colder (the other three regions).

4.2 Mean and Absolute Extreme Air Temperatures

As results from investigations conducted by Przybylak (1996a, 1997a), the patterns of spatial distribution of mean 40-year normal (jTMJ and extreme (7" and 7*min) air temperatures in the Arctic are similar in all seasons and for the whole year. The differences, of course, occur only in the magnitudes of temperatures. Usually the mean seasonal T and T . are or j mix mm warmer and colder respectively than Fmr n by about 4°C, and for the year as a whole by about 3°C. The only exception to this rule is the Arctic Ocean in summer, mainly in July, when the prevailing melting of snow and sea ice significantly reduces these differences. From the above-mentioned reasons only the mean annual spatial distribution of T and T is shown here (Figu-

re 4.5). For Greenland, unfortunately, such maps do not exist, but one can probably assume that the relationships described between the thermal parameters mentioned earlier also occur here. In particular years the highest deviations from the norm of mean extreme air temperatures are noted for winter (3-8°C) and the lowest for summer (1-3°C for T . and for T ).

Annual mean temperatures have anomalies of values similar to those of summer temperatures (Przybylak 1996a, 1997a). The spatial distribution of the variability parameter (a) computed for mean seasonal and annual 7* and Tmm is very similar to that of (Figure 4.7). Przybylak (1996a) found that rm„ has slightly higher, and Tmm slightly lower o than 71 .

The influence of cloudiness on Tmax is opposite in warm (June - September) and cool (October - May) half-year periods (Table 4.2). In summer the highest Tmax is connected with clear days and the lowest with cloudy days. Positive anomalies during clear days (see Table 4.2), are especially high (3-7°C) in the most continental part of the Russian and Canadian Arctic. They are much lower in the western and central parts of the Atlantic region (1-2°C). An increase in cloudiness in summer leads to a cooling of the whole Arctic, but especially of the parts of the Arctic which are located near its southern border and are characterised by a high continentality of climate: the stations Naryan-Mar, Chokurdakh, and Coral Harbour A. For these stations the mean differences of Tmax between clear and cloudy days vary from 5°C to 7°C, while in the Norwegian Arctic (maritime climate) they only differ from l°C to 2°C (see Table 4.2). In the cool half-year, the influence of cloudiness on Tnm is opposite to that of summer i.e. an increased cloudiness leads to a warming of the Arctic. The positive anomalies of 7mix on cloudy days are the highest in winter (above 4°C) almost over the whole Arctic, except for the regions represented by the Jan Mayen and Mys Sfamidta stations. It is noteworthy that most of the Arctic (excluding the Siberian region and the western part of the Atlantic region) has higher positive anomalies on cloudy days in spring than in autumn. On clear days, the highest negative anomalies occur in autumn, except fur the Jan Maycn and Naryan-Mar stations. In the annual course the lowest differentiated influence of cloudiness on occurs at the turn of May/June and September/October, when the described relations between cloudiness and 7*nm change rapidly from one mode to another (see Figure 4 in Przybylak 1999).

Table 4.2. Mean seasonal anomalies of 7* (in °C) in the Arctic on clear (I). partly cloudy (2) and cloudy (3) days over the period 1951 1990 (after Przybylak 1999)

Generally speaking, the influence of cloudiness on 7V is roughly similar to that on Tmia, but there are also several important differences (compare Tables 4.2 and 4.3). One such difference is the opposite influence of cloudiness on 7V and on Tim in summer in the Norwegian Arctic and in the southern Canadian Arctic. During this season 7*miii is higher on cloudy days than clcar days (see Tabic 4.3). Moreover, positive anomalies of 7"min in the rest of the Arctic are significantly (2-3 or more times) lower than anomalies of T a (compare Tables 4.2 and 4.3).

Table 4.3. Mean seasonal anomalies of 7" (in °C) in the Arctic on clear (1), partly cloudy (2) and cloudy (3) days over the period 1951-1990 (after Przybylak 1999)

Season

Element

DAN*

JAN

HOP

NAR*

DIK*

CHO*

SHM*

RES**

COR**

CLY**

1

-3.3

-5.2

-8.4

-12.9

-6.9

-3.9

-6.1

-2.5

-1.9

-3.9

DJF

2

-0.3

-1.3

-1.9

-5.5

-1.8

-1.1

-1.1

0.2

-0.3

-0.3

3

5.4

I.I

5.2

6.1

4.6

4.1

3.4

5.8

9.2

6.1

Mean

-27.1

-7.8

-15.9

-21.3

-28.5

-36.7

-28.2

-35.0

-32.3

-30.4

1

-3.7

-1.2

-8,8

-10.7

-9.1

-5.8

-8.9

-6.1

-7.5

-5.8

MAM

2

-0.2

-1.6

-2.4

-2.7

^t.O

-0.9

-2.1

-1.3

-1.4

-1.1

3

4.1

1.1

4.3

3.6

4.6

5.3

5.2

9.0

9.2

7.0

Mean

-19.7

-5.5

-12.3

-10.4

-19.8

-21.3

-20.0

-25.5

-21.2

-22.4

1

0.8

-0.7

-0.3

1.8

4.4

1.6

0.9

1.5

-0.2

0.3

J J A

:

0.0

-0,6

-0.3

1.1

1.1

0.9

0,5

0.3

0.0

0.0

3

-0.3

0.2

0.1

-0.9

-0.4

-0.7

-0.3

-0.3

0.0

-0.1

Mean

-0.3

2.2

0.1

6.4

0.9

3.7

0.9

-0.5

2.1

-0.4

1

-4.2

-2.4

-13.0

-9.6

-15.1

-11.6

-8.9

-11.4

-12.5

-11.5

SON

2

-0.3

-0.9

-3.1

-3.3

-7.4

-4.6

-4.0

-3.4

-2.2

-2.2

3

4.2

0.4

1.9

2.4

4.1

4.9

2.6

6.9

5.3

3.6

Mean

-15.6

-1.6

-5.1

-5.2

-11.3

-15.8

-11.3

-17.8

-11.5

-11.3

Key: Mean - mean seasonal TV^; other explanations as in Table 4.2

Key: Mean - mean seasonal TV^; other explanations as in Table 4.2

In winter, the influence of cloudiness on both T and T is very simi-

miix mrn J

lar, but negative anomalies on clear days are lower in most of the Arctic in the case of 7V . In spring, the influence of cloudiness is significantly greater on 7\n than on Tinax. Negative (or positive) anomalies of 7\n on clear (or cloudy) days are clearly greater than anomalies of TmK. This means that an increase in cloudiness results in a much greater rise of T . than T during

this season, A similar situation is also present in autumn, although it is expressed slightly weaker than in spring.

Absolute minimum temperatures in the Arctic defined according to Atlas Arktiki (1985) occur on the Greenland Ice Sheet. Temperatures in the winter months (December-March) very often drop below -50°C. The lowest measured temperature occurs in the Northice station (-66.1°C, 9lh Jan. 1954). Slightly higher temperatures (-64.8°C) were noted in Eismitte (20,h March 1931) and Centrale (22,ld Feb. 1950). Outside Greenland, the absolute temperatures below -50°C occur over a large area of the Arctic characterised by the greatest degree of continentality (above 60-70%, Figure 4.2). The temperature drops below -50°C in the belt stretching from the central part of the Russian Arctic through the North Pole to the north-eastern part of the Canadian Arctic (see Gorshkov 1980, p. 44 or 45). Maxwell (1980) reported that the absolute lowest temperature in the Canadian Arctic prior to 1975 was recorded at Shepherd Bay (south of Boothia Peninsula) in February 1973 (-57.8°C). However, Sverdrup (1935) reported (see Table on p. K11) that in the area of Lady Franklin-Bay (in the north-eastern part of Ellesmere Island) the lowest noted temperature reached -58.8°C. The exact date when this temperature occurrcd is unknown (Sverdrup did not give such information), but analysing his Table 7 we can say that this temperature had to be noted during one of the following winters: 1871/72, 1875/76, 1881/82/83, 1905/1906 or 1908/09. The temperature -58.8°C is probably also the lowest temperature noted in the whole "lower" (without Greenland) Arctic. The absolute lowest temperature in the Northern Hemisphere, as we know, occurred in the Subarctic at Oimekon, where it reached -77.8°C (Martyn 1985). In summer, the absolute temperatures < 0°C occur over the entire Arctic. In the central Arctic these temperatures range from -8°C to -16°C (Gorshkov 1980). In Greenland they drop below 20°C and in June and August even below -30°C (see Putnins 1970, his Table XVIII).

The absolute maximum temperatures occur in summer and show a clear dependence on the latitude (see Gorshkov 1980), In the central Arctic they are always below I0QC and in the Arctic islands they rarely exceed 20°C. The highest recorded temperatures occur in the continental southernmost parts of the Arctic (especially in the western parts of the Canadian and Russian Arctic), where they can even exceed 30°C. The highest temperature in the continental part of the Canadian Arctic was recorded at Coppermine (30.6°C) (Rac 1951). In the Canadian Arctic Archipelago, the highest temperature occurred at Cambridge Bay (28.9°C, July 1930). In the Russian Arctic, the absolute maximum temperatures can also exceed 30°C (Gorshkov 1980). In the coastal region, between 45°E and 60°E, the temperature is even higher than 32°C. For example at Naryan-Mar station the highest recorded temperature in 1967— 1990 was equal to 33.9°C (10 July 1990). In winter, the highest temperatures never reach freezing point in the most continental part of the Arctic stretching from the central part of the Siberian region, through the central Arctic, to the eastern and northern part of the Canadian Arctic (see Gorshkov 1980). On the Greenland Ice Sheet, they are very rarely higher than -10°C.